A steel ball or a ceramic ball for a bearing is subjected to precise polishing processing in order to obtain a high degree of sphericity. In this polishing processing, the spherical object is polished using a grindstone or free abrasive grains and an oil-based or water-based coolant. Therefore, contamination such as coolant or polishing powder may in some cases adhere to a surface of the spherical object subjected to polishing processing, and thus, it is necessary to further perform a cleaning step in order to remove the contamination.
A method for cleaning a spherical object includes various methods depending on a size of the spherical object and the required degree of cleanliness. Examples of a general method for cleaning a spherical object include ultrasonic cleaning, brush cleaning, roll cleaning, hand-wash cleaning or the like. In the case of ultrasonic cleaning, a spherical object is cleaned by a shock wave generated by cavitation. In the case of brush cleaning, a spherical object is put into a disk-shaped cage and a surface of the spherical object is rubbed with a brush to thereby clean the spherical object. In the case of roil cleaning, a spherical object is rolled on a sponge or the like to thereby clean the spherical object. In the case of hand-wash cleaning, a spherical object is rolled with double-handed kneading or with a sponge and a hand to thereby clean the spherical object. In addition, as this type of method for cleaning a spherical object, Japanese Patent Laying-Open No. 7-100229 (PTD 1) describes a method for cleaning a spherical object while feeding the spherical object along a spiral guide member.